Epoxy resin compositions containing allylic bromide terminated polybutadienes, mixed with amine terminated polyamide curing agents just prior to application, have been disclosed as suitable replacements for molten metals such as automotive body solders in Anagnostou et al., U.S. Pat. No. 3,842,023. Payne, U.S. Pat. No. 3,412,046 discloses that arylsulfonium salts of simple anions may be employed as substitutes for tertiary amine catalysts in anhydride cured epoxy resin systems. Catalyzed epoxy resin compositions comprising epoxidic prepolymers and an aromatic diazonium salt of a complex halogenide are shown to be useful for coating and related applications at or near room temperature in Watt, U.S. Pat. No. 3,794,576. In this case, there is no need to mix immediately prior to use. Hardening is induced through heating or preferably through irradiation, as with ultraviolet (UV) light. Such epoxy resin materials are also hardenable by combination with radiation-sensitive aromatic sulfonium salts of complex halogenides, Crivello, U.S. Pat. No. 4,058,401, or with radiation-sensitive aromatic iodonium salts of complex halogenides, Crivello, U.S. Pat. No. 4,026,705. See also Barton, U.S. Pat. No. 4,090,936. Reducing agents, such as copper, tin, cobalt, and the like salts, and some acids have been reported to speed up the rate of cure of epoxy resin compositions in combination with aromatic onium salts. In addition, Crivello, U.S. Pat. No. 4,173,551 and copending Crivello application Ser. No. 940,564, filed Sept. 8, 1978, both of which are owned by the assignee of the present application. Such compositions can be flexibilized with polymers, such as polyether polyols or polyester polyols or with glycidyl ethers of alcohols, and filled with silica, talc, clay, glass fibers, hydrated alumina and the like, and applied to substrates, such as metal, rubber, and the like, for decorative, protective, insulating, sealing, and similar purposes. The foregoing patents and applications are incorporated herein by reference.
The UV-curable epoxy resin systems do, however, have a major disadvantage when heavily filled with mineral fillers, such as talc, and that is a lack of deep section cure. It is believed that this lack of cure is due to the inability of sufficient ultraviolet radiation to pass through the filler and give an adequate cure.
It has now been found that the problem of inadequate deep section cure can be overcome by the use of a catalyst combination which provides curing by both ultraviolet radiation and thermally. The thermal component of the catalyst precursor combination must be chosen carefully so that the UV catalyst does not interfere with the thermal catalyst and vice versa. Preferably, the cure speed of the thermal catalyst should be such that thermal cure is initiated by the heat given off by the same source (lamp) used to provide UV radiation, but this is not always essential. The major utility of the new discovery is in providing one-package putties to replace molten metal body solders in the manufacture of automobiles, and the like. The putty can be applied in the usual thicknesses to dents, dimples, gaps, etc; on the sheet metal, and then cured all of the way through by exposure to UV radiation and heat, in very short times, e.g., 1 to 15 minutes.